The Collaborative International Dictionary
Hygrometry
Hygrometry \Hy*grom"e*try\, n. [Cf. F. hygrom['e]trie.] (Physics) That branch of physics which relates to the determination of the humidity of bodies, particularly of the atmosphere, with the theory and use of the instruments constructed for this purpose.
Wiktionary
hygrometry
n. The measurement of the moisture content of gases, but especially of the humidity of the atmosphere